Physical And Numerical Simulation Of Inner Crack Healing In Metals

The Research on the mechanism of the internal crack healing in metals is an important basic work for improving metal quality and prolonging its lifetime, and it is very significant for developing the theory of materials. There is a broad engineering application background and potential benefits of economic and social as the main work of the key project "Inner crack healing in metal"supported by National Natural Sciences Foundation of China, physical and mathematic simulation were taken to study the internal crack healing in metals. On this basis diffusion thermodynamics and inner variable analysis in crack healing processing have been discussed. Physical simulation: sample preparation, in situ observation of inner crack healing, experiment research on inner crack healing process. Two methods were adopted to obtain the samples containing internal pre-cracks. One is plate impacting and the other is compressing drilled hole in column sample. It were found that the internal cracks in the samples of pure copper made by plate impacting consist of the micro-voids connected by micro-cracks and many dispersed micro-voids, while the internal cracks made by compressing drilled hole in the samples of pure iron, 20, 45, 16Mn and 5CrMnMo steel consist of lentoid primary cracks and spokewise secondary cracks. In situ observation of the internal crack healing on the section of pure copper sample under high temperature metallograph showed that the micro-voids of 10-100μm begin to be healed at the temperature of 750℃, and obviously healed at the temperature of 900℃. SEM analyze showed that the healed micro-voids consist of some agglomerate particles at the scale of micrometer and much smaller particles on these agglomerate particles. According to the above observation, the healing processing is proceeded from inner surface of holes in matrix to observation plane for opening holes of the sample. Conclusion can be drawn that the healing processing of closed holes in the sample will be done from inner surface to the center. After healing processing of the samples of pure iron, 20, 45, 16Mn and 5CrMnMo steel, the healing area of internal cracks made by compressing drilled hole was observed and analyzed. SEM analysis displayed that the fine structure exists in healing area is mostly ferrite and there exists many polyangular grains of several hundreds nanometer and precipitated particles which means that bulk diffusion resulted in the supersaturated healing area. X-ray analyze showed that the content of main elements Fe,Mn,S and Si in matrix, healing area and precipitated...